The invention relates to a punch arrangement for a press, in particular a rotary press, comprising at least one press punch having a punch head, a tool region and a punch shank extending between the punch head and the tool region, further comprising at least one punch guide having at least one guide bore in which the punch shank of the at least one press punch is guided in an axially movable manner and at least one variable length sealing sleeve at least partially surrounding the punch shank, which sealing sleeve is retained with its first end against the punch shank or against the tool region of the press punch. The invention further relates to a press and a rotary press.
It is known to provide a seal between a compression chamber of a press and a punch guide, in particular guide bores, via variable length sealing sleeves. Such an arrangement is disclosed, for example, in DE 295 16 577 U1. In this case, a sealing sleeve configured as a folding bellows is retained at its one end by an annular fastening portion in an annular groove of a press punch. At its other end, the sealing sleeve is also retained by an annular fastening portion in an annular groove of a retaining portion configured on the punch guide. The retaining portion with the annular groove protrudes downwardly from the guide bore of the punch guide.
In the known construction, the folding bellows has a relatively loose fit in the annular groove of the retaining portion protruding downwardly from the guide bore. With the rapid axial movements of the press punch during the operation of the press, therefore, the folding bellows may be released from the annular groove of the retaining portion. The seal between the compression chamber and the guide bore is thus no longer ensured, potentially resulting in damage to the punch guide and contamination of the pellets produced and thus to production waste. It may also result in compression of the released folding bellows. A further drawback of the known design is that the retaining portion limits the maximum stroke of the press punch. Moreover, in the known construction cleaning is relatively complex.
In certain applications, it is desirable to provide a so-called stripping element instead of a sealing sleeve. Such stripping elements are located in the region of the outlet of the guide bore facing the compression chamber and bear sealingly against the press punch in the peripheral direction of the punch shank. During the lifting movements of the press punch occurring during operation, the stripping element brushes over the surface of the punch shank in the axial direction and at the same time brushes away contaminants from the punch shank. In the known devices, the stripping elements are either pressed into a groove by their metal cage or by a suitable external geometry. In the known devices, the fastening devices for the stripping elements differ from the fastening devices for the sealing sleeves. As a result, changing between the sealing sleeves and the stripping elements is only possible in a complex manner. This applies, in particular, to rotary presses when the rotor is designed to remain in the tablet press. Generally, adapter rings are required for changing between the sealing sleeves and the stripping elements, which are only able to be mounted and dismantled using special tools. This leads to long changeover times and damage when used incorrectly.
Proceeding from the aforementioned prior art, therefore, the object of the invention is to provide a punch arrangement, a press and a rotary press of the type mentioned in the introduction, in which the operational reliability is increased, the maximum punch stroke is increased, the changeover is facilitated when changing between the sealing sleeve and the stripping ring and the changeover time required therefor shortened and the cleaning simplified.